What is the point of severe shaking when frightened or in shock?

Granted that the answer to this question will probably rest on whether you believe in evolutionary theory…but assuming that you do….

Something really awful happened to me earlier this evening. I returned home to find my ex-partner (of 5 years ago not Theo’s father!) waiting for me on my doorstep asking to come in. He is an alcoholic, was abusive emotionally and physically. He looked awful, pretty battered; he had blood down his nose, glasses were torn apart, he was drunk and slurring his words.

I haven’t seen him for years, this was completely out of the blue. I was terrified. I managed to get rid of him anyway in the process of getting verbal abuse and could feel myself beginning to shake, voice disappearing and legs crumbling beneath me. When I got me and my son into the house my whole body was convulsing and I struggled to stand up, I tripped over a few things and struggled to breathe. Was OK though after a while.

I want to know what the purpose of this physical response to the situation is? I don’t see how it can be productive at all because I felt physically ill and couldn’t have defended myself if I’d have tried… Was just lucky he walked away really. But my question is two fold really because…. I also have IBS and suffer when stressed…and of course my tummy is aching now four hours after the event, I feel sick…but lower down I’m cramping…and I’m wondering why this happens? How can this benefit me? What should I be learning from my body on this one?

Thanks all xxxx